Fluid contact coking in the presence of hydrogen produced by dehydrogenation of product gases



July 21, 1959 A. R. VANDER PLOEG 2,895,896

Nu 1N THE PRESENCE oF HYDROGE FLUID CONTACT COKI PRODUCED BYDEHYDROGENATION OF PRODUCT GASES Filed Deo. 1, 1954 United States PatentO FLUID CONTACT COKING IN THE PRESENCE F HYDROGEN PRODUCED BYDEHYDROGENA- TION OF PRODUCT GASES Alfred R. Vander Ploeg, Port Arthur,Tex., assignor to Texaco Ine., a corporation of Delaware ApplicationDecember 1, 1954, Serial No. 472,460

2 Claims. (Cl. 208-53) This invention relates to the cracking and cokingof hydrocarbon oils by contacting the oil with pulverulent or powderedcoke and is concerned with a process in which coke from the hydrocarbonreaction zone is subjected to combustion to provide hot coke forcontacting with the oil in the reaction zone.

The invention is directed to a process in which hydrogen is an essentialcomponent of the iluidizing gas in the reaction zone and to a method inwhich hydrogen is produced by contacting recycle gases with highlyheated coke from the combustion or burning zone.

In accordance with the invention hydrocarbon oil such as heavy petroleumresidual stock is contacted with the coke particles in a reaction zonemaintained under fluidized conditions to effect cracking and coking,coke is withdrawn from the reaction zone and is fluidized with air orother oxygen gas to eiect combustion under high temperature conditionsso as to produce highly heated coke which is contacted with recyclegases with suicient reaction time to effect conversion to hydrogen andthe eiluent products from the hydrogen-forming zone are delivered to thehydrocarbon reaction zone, the formed hydrocarbon constituting anessential uidizing agent in the latter reaction zone.

The production of hydrogen by contacting the recycle gases with thehighly heated coke from the combustion or burning zone makes available arelatively cheap source of hydrogen, and the presence of hydrogen in thecoking zone is highly beneficial in the coking operation. The hydrogeninhibits coke formation so that less coke is formed with a consequentincrease in yield of valuable liquid products such as gas oil. Moreover,the presence of the hydrogen prevents the degradation of the gas oilproduct which commonly accompanies the ordinary coking operation andproduces a gas oil of improved qualities for subsequent catalyticcracking.

For the purpose of more fully explaining the invention reference is nowhad to the accompanying drawing which is an elevational ow diagram of apreferred embodiment thereof.

In the drawing is a reactor in which the hydrocarbon oil is subjected tofluid contact cracking and coking and 11 is the coke burner or calcinerin which coke from the reactor is subjected to combustion. The oil to besubjected to cracking and coking is admitted through a line 12 and oneor more branch lines 13 `for discharging the oil into the dense bed ofthe iluidized mass. Fluidization is maintained in the reactor 10 bymeans o-f the entry of vapors and gases including hydrogen as isexplained hereinafter. The hydrogen-containing gases are relied on asthe essential uidizing agent but a small amount of steam may be admittedto the bottom of the reactor for the purpose of stripping hydrocarbonsfrom the coke. The evolved vapors and gases are removed from the dilutephase through a vapor line 14.

Coke is withdrawn from the dense phase of the reactor through astandpipe 15 and is transported in a current of air or otheroxygen-containing gas, admitted by a line 16, through a transfer line 17to the coke burner 11 wherein the coke is subjected to combustion underhigh temperature fluidized conditions. Flue gases are removed throughVent 18 and the highly heated coke is withdrawn from the burner orcalciner 11 through a standpipe 19, a portion of the coke beingwithdrawn as product coke by a line 20. Due to the high temperatureconditions the coke withdrawn from the burner 11 is a low volatile, infact, a calcined coke.

The highly heated coke from standpipe 19 is picked up by a stream ofhydrocarbon gas ilowing in line 21 and the stream of gas with thedispersed coke is subjected to cracking and dehydrogenation to producehydrogen. This conversion to hydrogen is accomplished by having asuilicient time of reaction in the pipe reactor 21 tol effectsubstantial production of hydrogen. Alternately, the stream of gases anddispersed coke is diverted from the pipe reactor 21 to a reactionchamber 22 which affords an increased time of reaction. The gases incontact with the highly heated coke are subjected to reaction underlluidized conditions in the uplow reactor 22, the entire products owingthrough a line 23 and being returned to the transfer line 21 by whichthe iluidized stream of coke and reaction products including the formedhydrogen is delivered to the reactor 10.

In the fractionating system shown the vapors from the reactor ilowing inlline 14 are delivered to a primary fractionating tower 24, chargingstock such as reduced crude or other residual stock is introduced by aline 25 through heat exchanger 26 to the fractionator 24 and the bottomfraction comprising unvaporized charge and reux condensate is withdrawnby a line 27 and directed by pump 28 and line 12 to the reactor 10. Theoverhead vapors and gases from the tower 24 pass to a secondaryfractionator 29 for further fractionation. Gas oil is withdrawn from thelatter tower, cooled in exchanger 26 and withdrawn from the system by aline 30 for subsequent use in catalytic cracking or for other purposes.A portion of the gas oil may be directed by pump 31 as reflux in thefractionator 24. The vapors and gases from `fractionator 29 pass througha cooler 32 to a distillate accumulator or receiver 33. The gasoline ornaphtha product is withdrawn by a line 34, a portion being recycled bythe pump 35 as reflux for the tower 29.

Product gas leaves the accumulator 33 through a line 36. A portion ofthe gas is conducted by a line 37 and is directed by a compressor 38through a line 39 to the transfer line 21 for iluidzing and transportingcoke received from the standpipe 19 as has been explained. Generally thegas being recycled through line 39 or a portion thereof is passedthrough a preheating coil 40 before entering the line 21. The gas takenoff the accumulator 33 consists predominantly of the normally gaseoushydrocarbons together with some hydrogen. lf desired the gas may befractionated in order to segregate product hydrogen and so that therecycled gases will consist mainly of light hydrocarbons.

Temperatures in the coke burner or calciner are maintained at a veryhigh level such as 2000-2500 F. in order to supply sufficient heat forthe hydrogen forming step. A temperature of 1500 F. is about the minimumtemperature that can be used in the coke burner for this purpose andpreferably the temperature is maintained substantially above 1500 F. Thetemperature of the commingled coke and gas in the transfer line reactor21 and in the reactor 22 is held within a range of about 1200-20007 F.with residence times of 0.120.0 seconds to sustain an effectiveconversion to hydrogen. The lower temperatures with the longer contacttimes within these ranges favor the production of aromatics which may bedesirable to improve the anti-knock quality of the naptha product. Inthis way a higher octane naphtha can be produced than in the usual iluidcontact coking process while at the same time the cracking qualities ofthe gas oil product are not impaired due to the presence of the hydrogenin the reactor 10. The gas .recycle rate` is advantageously within arange of about 0.5-10.0 mols per mol of reactor charge. The process isconducted under such superatmospheric pressure as is required to obtainthe desired residence time in the hydrogen forming zone and to obtainthe beneficial effect of the hydrogen in the uidized coking zone.

The temperature in the cracking and coking reactor is reduced totemperatures that are usual for fluid contact coking operations.Satisfactory temperatures are in the range of about 950 to 1050 F.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

I claim:

1. The process of producing a superior gas oil adapted for catalyticcracking that comprises contacting a residual petroleum stock with cokeunder luidized conditions at cracking and coking temperature in areaction zone, passing coke from the reaction zone to a burning zone inwhich the coke is subjected to combustion at a temperature of at least1500 F., withdrawing coke at a temperature of at least 1500 F. from theburning zone, withdrawing vapors comprising hydrocarbon gas from saidreaction zone, dispersing said coke withdrawn from said burning zone insaid hydrocarbon gas and passing the dispersion through adehydrogenation zone at a temperature of about 1200 to 2000" F. for atime of about 0.1 to 20.0 seconds effecting dehydrogenation andformation of hydrogen, delivering eflluent from the dehydrogenation zonecomprising coke and hydrogen to the aforesaid reaction zoue to supplyheat thereto and maintain iiuidization therein in an atmosphere ofhydrogen and fractionating evolved vapors from said reaction zone toseparate said gas oil.

2. In the cracking and coking of hydrocarbon oils the process thatcomprises subjecting hydrocarbon oil to cracking and coking temperaturein a reaction zone in contact with coke under iiuidized conditions,withdrawing coke from the reaction zone and subjecting it to combustionin a burning zone at a temperature of at least 1500 F., withdrawingvapors comprising hydrocarbon gas from said reaction zone, withdrawingcoke at a ternperature of at least 1500 F. from the burning zone,dispersing said coke withdrawn from said burning zone in saidhydrocarbon gas and passing the dispersion at a temperature within therange of about 1200 to 2000 F. through a dehydrogenation zone whereinthe dispersion is subjected to dehydrogenation for about 0.1 to 20.0seconds, eccting formation of hydrogen and delivering eiuent from thedehydrogenation zone comprising coke and hydrogen to the aforesaidreaction zone to supply heat thereto and maintain uidization therein.

References Cited in the tile of this patent UNITED STATES PATENTS1,875,923 Harrison Sept. 6, 1932 2,471,104 Gohr May 24, 1949 2,600,430Riblett June 17, 1952 2,738,307 Beckberger Mar. 13, 1956 FOREIGN PATENTS709,583 Great Britain May 26, 1954

1. THE PROCESS OF PRODUCING A SUPERIOR GAS OIL ADAPTED FOR CATALYTICCRACKING THAT COMPRISES CONTACTING A RESIDUAL PETROLEUM STOCK WITH COKEUNDER FLUIDIZED CONDITIONS AT CRACKING AND COKING TEMPERATURE IN AREACTION ZONE, PASSING COKE FROM THE REACTION ZONE TO A BURNING ZONE INWHICH THE COKE IS SUBJECTED TO COMBUSTION AT A TEMPERATURE OF AT LEAST1500* F., WITHDRAWING COKE AT A TEMPERATURE OF AT LEAST 1500* F. FROMTHE BURNING ZONE, WITHDRAWING VAPORS COMPRISING HYDROCARBON GAS FROMSAID REACTION ZONE, DISPERSING SAID COKE WITHDRAWN FROM SAID BURNINGZONE IN SAID HYDROCARBON GAS AND PASSING THE DISPERSION THROUGH ADEHYDROGENATION ZONE AT A TEMPERATURE OF ABOUT 1200 TO 2000* F. FOR ATIME OF ABOUT 0.1 TO 20.0 SECONDS EFFECTING DEHYDROGENATION ANDFORMATION OF HYDROGEN DELIVERING EFFLUENT FROM THE DEHYDROGENATION ZONECOMPRISING COKE AND HYDROGEN TO THE AFORESAID REACTION ZONE TO SUPPLYHEAT THERETO AND MAINTAIN FLUIDIZATION THEREIN IN AN ATMOSPHERE OFHYDROGEN AND FRACTIONATING EVOLVED VAPORS FROM SAID REACTION ZONE TOSEPARATE SAID GAS OIL.